Study On High Brightness RGB LEDs And Illumination System In Projection Display Application

Since1900, with development of TV and computer media, network andinformation technology, in order to obtain large screen display, multi-color, highbrightness and high resolution, display industry has boomed as the main carrier ofimage information. It plays an increasingly important role in business, research,entertainment, education, etc. In the field of information, the output value of displayindustry is more than100billion dollars per year. The near few years is a criticalperiod for the structure adjustment of display device markets. Projection displaytechnology based on micro-display panels has the advantages such as no-radiation,large-size display and digitalization. It has played increasingly important role in thedisplay industry. It represents the development direction of future display technology,which is any flat surface can be a screen at any place. Currently, projection displaysystems typically utilize ultra high performance (UHP) lamp as the light source. It hasmany disadvantages such as volume, color gamut and life time although it has highbrightness. In contrast to UHP lamps, LED has smaller size, longer lifetime, largercolor gamut, lower cost, lower driving voltage, shorter response time, environmentallyfriendly, etc. It has been widely used in general lighting, special lighting, LCDbacklights, etc. and it has been gradually accepted as an alternative light source inprojection display application. Compared to UHP lamps, LED has low output luminous flux, which is a keyreason why LED can’t replace UHP lamp in the projection display. In addition, UHPlamp is a point light source and its optical solution is mature, but LED is a surface lightsource with Lambertian radiation pattern which makes it difficult to collect the lightefficiently. If LED’s light utilization efficiency is not high in projection display, all theadvantages of LED mentioned above will be meaningless. The objective of this paperis to solve these two problems.The development of LED chips and packaging structure was researched in thispaper. According to the requirements of illumination system in projection display, thepackaging structure of multiple-LED array was designed, which effectively solves theheat dissipation problem and low brightness problem of single-LED. RGBmultiple-LED arrays were packaged and their performances were characterized. Theexperimental results show that for RGB LED light sources, their luminous flux is276lm,1020lm and176lm respectively.Based on the structure and radiation pattern of multiple-LED array package,circular compound parabolic concentrator(CPC), freeform light collection system andrectangular CPC were designed and optimized separately according to the principles ofnon-imaging optics. After comparing their performances, solid rectangular CPC wasfabricated as the collimator and collector. It has the advantages of small size, high lightcollection efficiency, acceptable output divergence angle and being matched with LEDdies and micro-display panels. It was combined with multiple-LED array package andRGB multiple-LED modules for projection display application were fabricated. Theirperformances were characterized and the results show that for RGB LED modules,their output luminous flux is410lm,1165lm and181lm respectively. The divergenceangle of the light beam exiting the multiple-LED module is±16°, which is inaccordance with the simulation results. Because the fabricated rectangular CPC is solid, there will be refraction on theoutput surface of the CPC, which will increase the output divergence angle of lightbeam and decrease the light utilization efficiency in the projection display system. Inorder to overcome this shortcoming, hollow rectangular CPC was designed, optimizedand fabricated. Multiple-LED module with the hollow rectangular CPC was fabricatedand the performances were characterized. The experimental results show that thecollection efficiency of hollow CPC is85%and the output divergence angle of lightbeam is±12o, which is in accordance with the simulation results and will improvethe light utilization efficiency of projection display system.Based on the hollow rectangular CPC, an illumination system solution for LEDprojection display application was presented and the light utilization efficiency wasanalyzed, which will be of significance for the design and fabrication of illuminationsystem in projection display.